One known batch-type dryer which is promoted for drying sludge, specifically metal hydroxide sludge, employs an upwardly-opening channel-like drying chamber having an auger rotatably supported therein for agitating the sludge during the drying process. This drying chamber is defined by a generally U-shaped sidewall which opens upwardly and is closed at opposite ends. This sidewall has a bottom wall part which is of an arcuate configuration generated through an angle of about 180.degree., the center of which also defines the rotational axis for the elongate mixing auger. The arcuate bottom wall, after extending through this 180.degree. angle, integrally joins to generally parallel sidewalls which project upwardly in a vertical direction. The sidewalls at their upper ends define a top opening which is disposed substantially within a horizontal plane, which opening permits material to be deposited into the drying chamber. The mixing auger has blades which run in close relationship to the arcuate bottom wall part so as to effectively wipe the sludge from the wall and effect agitation thereof. A steam jacket extends around solely the arcuate bottom wall part to effect heat transfer through the wall to effect drying of the sludge. This general arrangement is diagrammatically illustrated by FIG. 6.
With this prior art dryer, and as is typical with dryers of this general type, a batch of wet material (specifically sludge) is deposited into the dryer chamber so as to fill the chamber up to about the horizontal plane passing through the rotational axis of the agitator (the plane 35' in FIG. 6), whereby the material substantially fills the arcuate bottom wall part. This sludge often initially has a consistency similar to clay, and during initial drying and working, the material may have a consistency more closely resembling peanut butter, until the material is more thoroughly dried to more closely resemble a granular material. Because of these properties, the material has a tendency to stick or adhere to the sidewall of the drying chamber, and for this reason the blades of the rotary auger 51' must rotate close to and hence effectively scrape the material from the surface of the arcuate wall. The natural rotation of the auger (counterclockwise in FIG. 6) causes the material to assume a profile substantially as illustrated by the dotted line 80' in FIG. 6. That is, the level of the material in the drying chamber falls significantly below the horizontal plane 35' on the side of the rotor which is moving downwardly, and conversely some of the material tends to accumulate above the rotor adjacent the sidewall 32' on the side of the rotor which is moving upwardly, thereby accumulating a mass of material 81' which is disposed outside the rotational path of the auger. While a system of the type described above and diagrammatically illustrated by FIG. 6 is commonly utilized and has been believed to operate in a satisfactory manner, nevertheless evaluation of this prior art system reveals that the structural and functional relationships are less than optimum.
More specifically, in evaluating batch-type dryers of this type, it is believed that the most effective heat transfer and hence efficient drying of sludge occurs due to the heat which is transmitted directly through the arcuate bottom wall part 29' so as to effect direct heating of the material which contacts the inside of this wall, but at the same time this heated material must be continuously scraped away from the wall and agitated so as to not only permit more uniform and efficient heating of the entire mass of material, but to also prevent "baking" of the material unto the wall. With this prior art arrangement of FIG. 6, however, the material tends to assume a profile similar to and anywhere in the range between that approximated by the lines 80' and 80". That is, the material on one side of the rotor drops below the plane 35' by anywhere from a minimum angle of about 15.degree. to a maximum angle which approaches about 90.degree.. Thus, the effective heat transfer area over the bottom arcuate wall 29' is reduced by a significant extent which may be up to at least 45.degree. and as much as 85.degree. of the overall 180.degree. extent of this bottom wall. At the same time, the mass 81' or 81" of material which collects above the rotor cannot be as effectively heated and dried since this mass 81' or 81" tends to strongly adhere or stick to the sidewall 32' and does not readily fall back into the rotor, whereby it thus is not properly mixed and dried with the same degree of efficiency as the material located within the rotor profile. Further, some prior art dryers of this type do not heat the vertical sidewalls so that very little drying of the material in the mass 81' or 81" occurs. While other prior art dryers extend the heat exchanger upwardly so as to heat these sidewalls, then such heating can have a detrimental effect since the mass 81' or 81" tends to securely adhere to this sidewall and this often results in overheating and hence baking of the outer layer of the material which directly adheres to the sidewall. This large mass 81' or 81", whether disposed adjacent a heated or nonheated sidewall, is detrimental to the overall drying efficiency.
Accordingly, the improved dryer of the present invention is designed to improve upon and significantly overcome the aforementioned disadvantages.
In the dryer of this invention, the drying chamber is defined by a sidewall having the same general configuration as the prior art except that the complete chamber is oriented so that its upwardly-opening direction is inclined at a substantial angle to the vertical. This results in both the 180.degree. arcuate bottom wall having its top plane disposed at a predetermined angle relative to the horizontal, and the upwardly projecting parallel sidewalls also extending at this same predetermined angle relative to the vertical. The rotor is rotated in a direction such that the side thereof having upward motion is located above the horizontal plane, and the rotor side having downward motion is located below the horizontal plane. Hence, after filling the rotor about one-half full with material, the rotor rotation causes the material to assume a sloped orientation similar to that in a conventional prior art dryer, but this sloped orientation is such that the bottom arcuate portion still remains substantially full of material. Effective heat transfer thus occurs throughout substantially the complete 180.degree. bottom arcuate wall, thereby significantly increasing the overall heating and drying efficiency. At the same time, the mass of material which accumulates above the output side of the rotor is itself normally of significantly less quantity since it is accumulating beneath the upwardly sloped sidewall and more directly overlies the center of the rotor. These factors, coupled with the slope of the sidewall, tends to minimize the adherence of the mass to the sidewall and thus facilitates the return of this material back into the rotor. This also increases the overall heat transfer and drying efficiency.
With this improved dryer, as briefly explained above, the opening defined at the upper edges of the sidewall is also disposed within a plane which slopes downwardly from the horizontal at said predetermined angle, whereby this facilitates sideward loading of the drying chamber, either manually or by means of a fork lift or other suitable equipment.
Other objects and purposes of the present invention will be apparent to permit persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.